Trans Diagnose on Caddy

OK guys. Looking for some input here. Have been shopping for a torque convertor for the 4l60E in the Caddy to correct a lock-up shutter but some of you suggested doing the line pressure test first before investing in a new torque. Connected one up this morning and the following is the results:

1. Park, OD pressure about 55 PSI at idle and 65 to 70 at slight throttle, brakes on.

2. Reverse only goes up to 75 or 80 at idle and can get it up to 90 PSI with slight throttle, brakes on.

3. Full throttle in second gives me 200 PSI but the needle fluctuates up there. Not much but it is a concern.

After reading the ISSF thread, I can assume the line pressure is too low but I am running on old fluid. Will do a complete change and try again. My concerns are the reverse pressure and the on idle pressure in drive. Apparently changing the boost valve will raise the rev pressure but by how much? Does 15 PSI low at base pressure indicate a bad pump? Could programming alter the pressures enough to compensate and if so will it correct the lock-up shutter?

The tranny has alot of miles so won't be suprised if it does indeed need a re-build, but if I can get by with this one for a while it would be better. The fluid is clean and there is no indication of adverse wear. It shift smoothly and does everthing its supposed to at the right time. The only obvious symptom is the lock-up shuttter.

Would appreciate your input here.

Bill

drop the valve body , make sure the force motor screen is clean,.new filter with deep pan,. add the oversize sonnax .490 boost valve,. then check pressures,. the bigger valve will help
do the transgo kit while its open,. the re-program it,.
'course i,d wait to hear what joel says first,.

Nick
yrmv

who knows, who cares. Dump in the LubeGard first and see what happens. Everything else gets more expensive and time consuming from there.

(edit - see my post below)

sherlock9c1 wrote:

who knows, who cares. Dump in the LubeGard first and see what happens. Everything else gets more expensive and time consuming from there.

nice attitude,.from someone who is well respected for thier knowledge of 4l60e's,.and is always extolling the vitues of buying/using a pressure guage,.

That's what I get for being brief. Let me explain myself.

Part of the reason I was frustrated is because there are very, very few people who are willing to take a step-by-step approach to transmission diagnosis. At some point they always throw in the towel and either buy a new transmission or just start throwing parts at it. Bill, you are to be commended for taking such a structure diagnosis view towards fixing this problem.

When it comes to TCC shudder, the LubeGard fix has worked for a large number of folks. WHY it works, I don't know, and this is why I said "who knows, who cares." It either works by modifying the friction potential of the fluid, softening up the seals in the transmission so it seals better, or perhaps even by some other method. Is the TCC clutch material shot? Is the apply circuit leaky? Is the overall line pressure too low? You can only really answer the last question based on your line pressure gauge, but then you would also have to take readings from another 4L60E in identical condition and see if it ALSO exhibits TCC shudder to point the finger solely at line pressure.

Your transmission is even trickier to make a snap diagnosis on because base line pressure looks low at 55psi but yet it was able to hit 200psi at WOT so that tells me that physically it HAS the capability to put out good pressure. The reverse pressure is low but I'm personally hesitant to say that the boost valve will fix that because I put it in my wagon for the same reason and it didn't get the Reverse pressure that much higher than it was before.

Another option you could do is to replace the torque converter with a reman unit and put a new seal on the input shaft (the input shaft seal gets worn out over time). That's a lot of effort, which is the other downfall about step by step 4L60E troubleshooting.

So anyway, sorry Bill for shooting off a one-liner and sounding frustrated. Nick's advice is good too and goes along with the Transgo kit installation instructions (the HD2C kit includes a boost valve and forces you to check the filter screen for the EPC solenoid).

Seriously though, I'd try a fluid/filter change and then LubeGard or ShudderFix or whatever the product's name is called.

My original intent here was to diagnose a bad torque convertor. As the old saying goes "when your up to your butt in alligators, it's difficult to remember that the original job was to drain the swamp". Just didn't want to shell out $250 bucks for a convertor if the problem was in the tranny.

The tranny flush and new fluid is a no brainer but while I have the pan off, can I clean the EPC filter and change the boost valve without dropping the valve body? If I'm going to invest in the HD2 then I will also get the new torque and do the job right and install the kit with the tranny out on the bench. Never had much patience with finiky things while lying on my back, with tranny fluid dripping in my eyes.

If I can tighten up the hydraulics in this thing and re-program the thing to at least factory levels, it will tell me immediately if the torque was the problem all along. The extra 10 or 20 bucks for the boost valve (will see if I can source it locally) and a few minutes cleaning a screen is time and dollars well invested. On the other hand "you can't polish a turd". If the tranny is toast, it's toast. A new convertor and shift kit ain't going to cure it.

Thanks a bunch for your help.

Bill

convert2diesel wrote:

. On the other hand "you can't polish a turd".Bill

True,. but you could chrome it,.

throw a litre of brake fluid in there,.(used car dealer trick,. don't ask me how i know,.) drive it for a day,. see what happens,. if it cures the shudders whip a filter and fluid in it,. and you,re good to go,..

Much nicer reply joel,.sorry if i ruffled your feathers a little,.

Nick

Tried that but couldn't get it to marry up with the Flux Capacitor. The resonance discharge caused a minute amount of anti-matter to collide with the 2.93 gears in the axle, causing a microscopic black hole event horizon to open up, draining the gear oil and resulting in the catastrophic distruction of both ABS sensors.

Bill

shove a 4l80e under it,. problem solved,.

nick